The subject is always announced when it is time to start writing. The subjects are picked from a general consensus of people who wrote quizzes for previous Community Quiz Challenges. If you go to the Salty Dog and look at the thread for the October Quiz Challenge -- Start Your Keyboards, it will explain the Ocober subject and the rules. When you have launched the quiz, put a note in the thread for launched quizzes and the editors should take it from there.